Mandatory directives include the required enforceable “Train Control Data” for a train operating on controlled track. The Train Control Data includes information such as movement authorities, speed restrictions, and the like. This data must be transmitted from the controlling entity to the train both at the trip origin and while the train is en route.
Since this is critical train control data, the exchange of the data must be performed in a “vital” (i.e., safety critical) manner. Failure to deliver vital data can result in unsafe operation of a train. Furthermore, the data on-board must be verified as being current at a frequent rate to avoid operating with stale or missing data.
Transmission of this data occurs over a communications path that typically has a relatively limited bandwidth, yet must accommodate data exchanges between the controlling entity and all operating locomotives and equipped wayside devices. Furthermore, to react quickly to changes in the operating environment, it is important that communications latency is kept as low as possible.